Determination of large nematic pre-tilt in liquid crystal cells with mechanically rubbed photorefractive Ce:SBN windows

Sutherland, Richard L.; Cook, Gary; Evans, Dean R.

doi:10.1364/oe.14.005365

Cited by 25 publications

(10 citation statements)

References 11 publications

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“…The second key factor that determines the strength of beam coupling is the conductivity of the LC: in conductive LCs lateral currents are more effective at reducing the imposed electrical modulation. This is also exemplified by the photorefractive cells analyzed in [38]. These cells use a photorefractive crystal to generate a modulated electric field: the strength of the modulation is stronger in low ionic content LCs, presumably because lateral currents are less able to counteract the electric field modulation.…”

Section: B Bragg Versus Raman-nathmentioning

confidence: 99%

Light-activated modulation and coupling in integrated polymer–liquid crystal systems

et al. 2014

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We explore the transfer of an incident light pattern onto the liquid crystal (LC) bulk in a photorefractive cell through an integrated photoconducting layer that modulates the electric field applied to the device. The electrical properties and the strength of modulation are investigated as a function of the incident light intensity as well as the frequency and amplitude of the applied voltage, for two LCs with very different electrical conductivity. A simplified electrical model of the cell is proposed, demonstrating that the LC conductivity is a key factor determining the beam-coupling strength.

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Section: B Bragg Versus Raman-nathmentioning

confidence: 99%

Light-activated modulation and coupling in integrated polymer–liquid crystal systems

et al. 2014

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“…But apparently this is not the case. [10][11][12] Rather, this maximum occurs when the ratio of grating spacing to cell thickness is rather small.…”

Section: Introductionmentioning

confidence: 97%

“…One of the beams is amplified, and in a LC beam-coupling geometry the exponential gain coefficients can reach values more than two orders of magnitude larger than those in solid inorganic photorefractive crystals. [7][8][9][10][11][12] Many of these systems involve a thin LC sample between two photorefractive layers. This is the so-called "dual photorefractive window geometry," and can be contrasted with the "single photorefractive window geometry," in which a photorefractive slab is present on only one side of the liquid crystal cell.…”

Section: Introductionmentioning

confidence: 99%

Beam coupling in hybrid photorefractive inorganic-cholesteric liquid crystal cells: Impact of optical rotation

Reshetnyak

Pinkevych

Sluckin

et al. 2014

Journal of Applied Physics

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We develop a theoretical model to describe two-beam energy exchange in a hybrid photorefractive inorganic-cholesteric cell. A cholesteric layer is placed between two inorganic substrates. One of the substrates is photorefractive (Ce:SBN). Weak and strong light beams are incident on the hybrid cell. The interfering light beams induce a periodic space-charge field in the photorefractive window. This penetrates into the cholesteric liquid crystal (LC), inducing a diffraction grating written on the LC director. In the theory, the flexoelectric mechanism for electric field-director coupling is more important than the LC static dielectric anisotropy coupling. The LC optics is described in the Bragg regime. Each beam induces two circular polarized waves propagating in the cholesteric cell with different velocities. The model thus includes optical rotation in the cholesteric LC. The incident light beam wavelength can fall above, below, or inside the cholesteric gap. The theory calculates the energy gain of the weak beam, as a result of its interaction with the pump beam within the diffraction grating. Theoretical results for exponential gain coefficients are compared with experimental results for hybrid cells filled with cholesteric mixture BL038/CB15 at different concentrations of chiral agent CB15. Reconciliation between theory and experiment requires the inclusion of a phenomenological multiplier in the magnitude of the director grating. This multiplier is cubic in the space-charge field, and we provide a justification of the q-dependence of the multiplier. Within this paradigm, we are able to fit theory to experimental data for cholesteric mixtures with different spectral position of cholesteric gap relative to the wavelength of incident beams, subject to the use of some fitting parameters. V C 2014 AIP Publishing LLC.[http://dx

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“…For the LC systems, very strong two-beam energy transfer between two coupled beams has been observed with gain coefficient values more than two orders of magnitude larger than those in solid inorganic photorefractive crystals. [7][8][9][10][11][12][13] Until recently it has only been possible to operate in the Raman-Nath regime, for which the sample thickness is less than the grating thickness. In this case the coupled beams generate multiple order diffracted beams that leads to limited technological applicability of the effect.…”

Section: Introductionmentioning

confidence: 99%

“…[10][11][12][13] In discussing the formation of a director grating in hybrid organic-inorganic photorefractives, the authors of papers 15,16 supposed that the light-induced space-charge electric field penetrating a ipinkevych@gmail.com from photorefractive substrates into LC couples with the director through the LC static dielectric anisotropy. However, this supposition predicts the maximal energy transfer at grating spacings comparable with the LC cell thickness, which contradicts experimental results [10][11][12] showing that this maximum occurs when the ratio of the grating spacing to cell thickness is rather small. The authors of paper 17 proposed that director grating formation in hybrid organic-inorganic photorefractives is governed by the interaction of the space-charge field with the LC flexoelectric polarization, rather than by static dielectric anisotropy coupling.…”

Section: Introductionmentioning

confidence: 99%

Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

et al. 2016

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We develop a theory describing energy gain when two light beams intersect in a hybrid nematic liquid crystal (LC) cell with photorefractive crystalline substrates. A periodic space-charge field induced by interfering light beams in the photorefractive substrates penetrates into the LC layer and reorients the director. We account for two main mechanisms of the LC director reorientation: the interaction of the photorefractive field with the LC flexopolarization and the director easy axis at the cell boundaries. It is shown that the resulting director grating is a sum of two in-phase gratings: the flexoelectric effect driven grating and the boundary-driven grating. Each light beam diffracts from the induced gratings leading to an energy exchange between beams. We evaluate the signal beam gain coefficient and analyze its dependence on the director anchoring energy and the magnitude of the director easy axis modulation.

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Determination of large nematic pre-tilt in liquid crystal cells with mechanically rubbed photorefractive Ce:SBN windows

Cited by 25 publications

References 11 publications

Light-activated modulation and coupling in integrated polymer–liquid crystal systems

Light-activated modulation and coupling in integrated polymer–liquid crystal systems

Beam coupling in hybrid photorefractive inorganic-cholesteric liquid crystal cells: Impact of optical rotation

Two beam energy exchange in hybrid liquid crystal cells with photorefractive field controlled boundary conditions

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